Non-invasive diagnostics for ventricle assist device

ABSTRACT

A circulatory assist system has a pump with a motor coupled to rotate the pump at a selectable speed. A controller drives the motor at a target speed and collects blood flow measurements during operation of the pump. An impaired flow condition is identified when a plurality of successive blood flow measurements are between an expected minimum flow and a low flow threshold, such that the low flow would necessitate issuing an alert. During the impaired flow condition, it is detected whether an inflow obstruction exists by determining whether a reduction in speed of the pump is correlated with a predetermined increase in the blood flow measurements. If the inflow obstruction is detected, then the speed of the pump is further reduced to further increase the blood flow measurements.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates in general to blood circulatory assistdevices, and, more specifically, to autonomous control of a pump tomaintain optimum blood flow under a variety of conditions includingpartial obstructions and low blood volume.

Many types of circulatory assist devices are available to either shortterm or long term support for patients having cardiovascular disease.For example, a heart pump system known as a left ventricular assistdevice (LVAD) can provide long term patient support with an implantablepump associated with an externally-worn pump control unit and batteries.The LVAD improves circulation throughout the body by assisting the leftside of the heart in pumping blood. One such system is the DuraHeart®LVAS system made by Terumo Heart, Inc., of Ann Arbor, Mich. Oneembodiment of the DuraHeart® system may employ a centrifugal pump with amagnetically levitated impeller to pump blood from the left ventricle tothe aorta. An electric motor magnetically coupled to the impeller isdriven at a speed appropriate to obtain the desired blood flow throughthe pump.

A typical cardiac assist system includes a pumping unit, electricalmotor (e.g., a brushless DC motor integrated into the pump), driveelectronics, microprocessor control unit, and an energy source such asrechargeable batteries. The system may be implantable, either fully orpartially. The goal of the control unit is to autonomously control thepump performance to satisfy the physiologic needs of the patient whilemaintaining safe and reliable system operation. A control system forvarying pump speed to achieve a target blood flow based on physiologicconditions is shown in U.S. Pat. No. 7,160,243, issued Jan. 9, 2007,which is incorporated herein by reference in its entirety. Thus, atarget blood flow rate may be established based on the patient's heartrate so that the physiologic demand is met. The control unit mayestablish a speed setpoint for the pump motor to achieve the targetflow. Whether the control unit controls the speed setpoint in order toachieve flow on demand or whether a pump speed is merely controlled toachieve a static flow or speed as determined separately by a physician,it is essential to automatically monitor pump performance to ensure thatlife support functions are maintained.

The actual blood flow being delivered to the patient by the assistdevice can be monitored either directly by sensors or indirectly byinferring flow based on motor current and speed. Despite the attempt bythe control unit to maintain a target flow, various conditions such asobstructions of the inflow conduit or outflow conduit from the pump, lowblood volume due to dehydrations, or other problems may cause the bloodflow to decrease. Low flow and no flow alarms are conventionallyemployed to indicate conditions when the blood flow through the pump hasinadvertently fallen below a low flow threshold or a no flow threshold,respectively. The alarms may comprise warning sounds, lights, ormessages to allow the patient or caregiver to take corrective action. Inorder to provide a greater safety margin, it would be desirable toidentify and correct flow problems before the low flow or no flowthresholds are reached.

SUMMARY OF THE INVENTION

In one aspect of the invention, a method is provided for controlling apump motor in an assist device for pumping blood of a patient. An actualpump flow value of the pump motor is monitored during pumping of theblood by the assist device. An expected minimum pump flow value isdetermined corresponding to nominal pump operation for the monitoredspeed and current flow. When the actual pump flow value is greater thanthe expected minimum pump flow value, a target speed of the pump motoris set according to predetermined criteria (which may comprise apredefined setpoint as determined by a physician, for example). When theactual pump flow value is less than the expected minimum pump flow valuefor at least a first diagnostic wait time, a pump flow diagnostic stateis entered.

In an embodiment, the pump flow diagnostic state comprises entering alow pump flow state if the actual pump flow value is less than a lowflow threshold for at least a low flow wait time. The low flow thresholdis less than the expected minimum pump flow value, and the low pump flowstate includes generating a low flow warning. A no pump flow state isentered if the actual pump flow value is less than a no flow thresholdfor at least a no flow wait time. The no pump flow state includesgenerating a no flow warning, wherein the no flow threshold is less thanthe low flow threshold, and wherein the no flow wait time is less thanthe low flow wait time. An obstructed flow diagnostic state is enteredif the actual pump flow value is less than the expected minimum pumpflow value for at least an obstruction diagnostic wait time, wherein theobstruction diagnostic wait time is greater than the low flow wait time.

In an embodiment, the obstructed flow diagnostic state comprisesselectably modifying the target speed of the pump motor and monitoringthe resultant actual pump flow value. An inflow obstruction is detectedif a reduction in target speed is correlated with a predeterminedincrease in the resultant actual pump flow value. If an inflowobstruction is detected, then the target speed is selectably decreasedto a new target that substantially maximizes the actual pump flow value.

In an embodiment, the obstructed flow diagnostic state comprisesdetecting an outflow obstruction if a reduction in target speed iscorrelated with a predetermined decrease in the resultant actual pumpflow value. If an outflow obstruction is detected, then the target speedis selectably increased to a new target until either a predeterminedmaximum speed or an actual pump flow value substantially equal to theexpected minimum pump flow value is obtained.

In an embodiment, changes in pulsatility associated with the modifiedspeed of the pump motor are also used to detect an inflow or outflowobstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a circulatory assist system of a typeemploying the present invention.

FIG. 2 is a graph showing changes in volumetric flow occurring duringoperation of a circulatory assist system.

FIG. 3 is a flowchart showing one preferred method of the invention.

FIG. 4 is a graph illustrating certain changes in flow and pulsatilitythat may be associated with changes in pump speed under certainconditions.

FIGS. 5 and 6 are graphs showing large and small flow increases that maybe associated with a reduction in pump speed.

FIG. 7 is a matrix showing general correlations of pump speed, flow, andpulsatility with inflow and outflow obstructions.

FIG. 8 is a more detailed decision matrix for one preferred embodiment.

FIG. 9 is a graph showing pump speed adjustments and resultant changesin flow when correcting for a detected obstruction.

FIG. 10 is a flowchart showing a further method of the invention.

FIG. 11 is a state diagram corresponding to another preferredembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a patient 10 is shown in fragmentary frontelevational view. Surgically implanted into the patient's abdominalcavity 11 is the pumping portion 12 of a ventricular assist device. Aninflow conduit 13 conveys blood from the patient's left ventricle intothe pumping portion 12, and an outflow conduit 14 conveys blood from thepumping portion 12 to the patient's ascending thoracic aorta. A powercable 15 extends from the pumping portion 12 outwardly of the patient'sbody via an incision to a compact controller 16. A power source, such asa battery pack worn on a belt about the patient's waist, and generallyreferenced with the numeral 17, is connected with controller 16.

Each of the conduits 13 and 14 may include a tubular metallic housingproximate the pumping portion 12 which may connect to elongated segmentsextending to the heart and ascending aorta, respectively. At the end ofinflow conduit 13 connected to the patient's heart (preferably at theapex of the left ventricle), and at the end of outflow conduit 14connected to the ascending thoracic aorta, the conduits are generallyattached to the natural tissue by sutures through the use of a sewingring or cuff so that blood flow communication is established andmaintained. The distal end of the inflow conduit 13 is inserted throughthe ventricle wall and into the heart in order to establish blood flowfrom the heart to the pumping portion 12.

FIG. 2 illustrates a target flow Q_(Target) at 20 and an actual flowvalue 25 that varies over time. A no flow threshold 21 and a low flowthreshold 22 define no flow region 23 and low flow region 24,respectively, wherein appropriate alarms are generated by a pump controlunit whenever actual flow dips into these regions. The trajectory ofactual pump flow value 25 may fall to a value below an expected minimumflow threshold 26 into a respective diagnostic region 27. Expectedminimum flow threshold 26 may be obtained from a lookup table or a modelbased on empirically derived flow profiles that result from variousinflow or outflow obstructions or various reductions in blood volume.The present invention is configured to detect operation in region 27 andto take steps to identify a potential cause and a remedy in order toincrease flow if possible.

When the actual flow falls below an expected minimum flow that should bepresent in view of the operating speed of the pump (i.e., assuming noobstructions and proper blood volume), the present invention enters adiagnostic state for identifying a potential cause of the impaired flowsuch as a partial or complete obstruction of the inflow conduit or theoutflow conduit, or a condition wherein a flow is saturated for a givenpump speed due to a limited blood volume resulting from dehydration,etc.

As shown in FIG. 3, a method of the invention begins in step 30 whereina physician or other medical practitioner configures target values andperformance limits pertaining to blood flow rate and pump speed to beprovided for a particular patient. The circulatory assist device thenmonitors for physiological conditions such as heart rate or pump pulserate in step 31. In step 32, a target flow rate and a target speed(i.e., setpoint speed) are determined and used for controlling thesystem as known in the art. Alternatively, a speed setpoint may bedetermined according to other predetermined criteria such as a setpointconfigured according to a static value chosen by a physician for theparticular patient. A check is performed in step 33 to determine whetherthe actual (i.e., indirectly estimated) pump flow value (eLPM_(pump)) isless than an expected minimum pump flow value (LPM_(ExpMin)) for greaterthan a diagnostic wait time (T_(FlowDiagWait)). As mentioned above,eLPM_(pump) is an estimated average pump flow for a given pump speed. Ifnot, then a return is made to step 31 and pump operation continuesnormally with the pump speed being determined by a target flow that isset according to physiological conditions.

If the actual pump flow value is less than the expected minimum flowvalue in step 33, then a check is made in step 34 to determine whetherthe actual flow is less than a low flow threshold (LPM_(LowFlow)). Inparticular, step 34 preferably requires that the actual flow value beless than LPM_(LowFlow) for greater than a predetermined low flow waittime (T_(LowFlowWait)). When eLPM_(pump)<LPM_(LowFlow) then a low flowwarning is generated in step 35. A low flow state is then entered whilethe low flow warning continues. Checks are made in step 36 to determinewhether the actual flow value has risen above the low flow threshold forgreater than the low flow wait time, and a check is made in step 37 todetermine whether the actual flow value is less than a no flow threshold(LPM_(NoFlow)) for at least a no flow wait time (T_(NoFlowWait)). Thevalue of T_(NoFlowWait) is less than the value of T_(LowFlowWait) sothat detection of a no flow condition has priority. If the actual flowvalue rises above the low flow threshold, then the warning is turned offin step 38 and a return is made to step 34. If an actual flow valuefalls below the no flow threshold for the no flow diagnostic wait time,then a no flow warning is generated in step 40 to indicate that agreater urgency of taking corrective action. While in a no flow warningstate, a check is made in step 41 to determine whether the actual flowvalue rises above the no flow threshold for longer than the no flow waittime. When it does, the no flow warning is turned off in step 42, thelow flow warning is turned off in step 38, and a return is made to step34.

When step 34 determines that the actual flow value has not stayed belowthe low flow threshold for the low flow diagnostic wait time, then acheck is made in step 43 to determine whether the actual flow valuestays below the expected minimum flow value for at least an obstructiondiagnostic wait time (T_(ObsDiagWait)) which is longer than both the lowflow diagnostic wait time and the no flow diagnostic wait time. If not,then a check is made in step 44 to determine the actual flow value hasrecovered above the expected minimum flow value for at least thediagnostic wait time (T_(FlowDiagWait)), and if so, then a return ismade to step 31 for nominal pump control. If the condition is not truein step 44, then a return is made to step 34 for continuing to monitorfor either a low flow condition or an obstructed condition. When thecondition in step 43 is satisfied then the method proceeds to step 45wherein a potential obstruction is diagnosed as described below.

The present invention is based in part on an observation that a nominalreduction in pump speed generally results in an increase in flow if aninflow obstructions exists. As shown in FIG. 4, a pump is operating at afirst speed at 50, but then a speed reduction 51 to a lower speed 52 isdeliberately introduced. After a sufficient time to allow flow tostabilize at a new value for measurement, speed then increases at 53back to the original speed at 54. An actual pump flow Q has an originalvalue at 55 will rise to a higher flow at 56 during a reduced pump speedat 52 in the event that an inflow obstruction exists. If an outflowobstruction exists, then the actual flow instead decreases as shown at57 during the time of reduced pump speed 52.

The change in pump speed may also affect the pulsatility index (e.g.,the difference between the maximum and minimum flows divided by theaverage maximum flow) such that an initial pulsatility at 60 decreasesto a value at 61 in the presence of an inflow obstruction when pumpspeed is reduced at 52. On the other hand, in the presence of an outflowobstruction the pulsatility will increase at 62 during the speedreduction. Inspection of the change in flow resulting from a deliberatespeed reduction may be sufficient to differentiate between an inflowobstruction and an outflow obstruction, but it may be coupled with aninspection of the change in pulsatility to potentially improve anidentification.

The diagnostic relationships employed by the present invention are shownin greater detail in FIGS. 5 and 6. FIG. 5 shows an inflow obstructionwherein a pump speed RPM_(setpoint) and a pump flow eLPM_(pump) aremeasured at a first time t₁. Pump speed is reduced by a predeterminedspeed of RPM_(ObsDiag) at a time t₂. At time t₂, the actual pump flowhas stabilized at a new value representing an increase by more than athreshold designated LPM_(ObsDiag), which indicates the presence of theinflow obstruction. In a preferred embodiment, a plurality of speedmodification trials of the type shown in FIG. 5 are repeated in order togather statistics for increasing a confidence level in detecting theinflow obstruction.

In FIG. 6, the actual flow through the pump increases during the speedreduction by an incremental flow that is less than the value ofLPM_(ObsDiag). In a preferred embodiment, the present invention does notdetect an inflow obstruction based on only the smaller increase in pumpflow, but may require simultaneous change in pulsatility index in orderto decide on the presence or absence of an inflow obstruction.

More specifically, an inflow or outflow obstruction may be determined asshown in FIG. 7. When pump speed is reduced and the resultant pump flowincreases while pulsatility index decreases, then an inflow obstructionis detected. On the other hand, when the speed reduction creates adecreased resultant flow together with an increased pulsatility index,then an outflow obstruction is detected.

The present invention may also distinguish between different levels ofconfidence in judging the presence of inflow and outflow obstructionsfor a saturated flow condition. For example, a large jump in flow beingproduced by a reduction in pump speed may always generate an indicationof an inflow obstruction. Depending on whether pulsatility experiences alarge drop or a small drop, the confidence of the inflow obstruction maybe characterized as either probable or possible, respectively. Asfurther shown in FIG. 8, a small jump in flow may correlate with alikely inflow obstruction if the pulsatility also experienced a largedrop. If both the jump in pump flow and the drop in pulsatility aresmall (i.e., less than respective thresholds), then the diagnosticdecision may correspond to a “no call” with respect to whether there isany obstruction or a saturated flow.

When a reduced speed generates neither a large change in flow nor alarge change in pulsatility, then a saturated flow may be detected. Inthe presence of a saturated flow, it may be desirable to reduce pumpspeed to the lowest value that maintains the current flow value.

An outflow obstruction may be detected according to FIG. 8 when a largedrop in the flow is correlated with the reduction in pump speed. If thelarge drop in flow occurs with a large jump in pulsatility, then anoutflow obstruction is probable. If associated with a small jump inpulsatility, then an outflow obstruction is classified as possible. Whena small drop in pump flow occurs with a large jump in pulsatility, thenan outflow obstruction is classified as likely, but if coupled with asmall jump in pulsatility then no call is made.

Based on the confidence with which either an inflow or an outflowobstruction is detected, corresponding measures can be taken to attemptto provide a greater flow or even restore the flow at least the expectedminimum flow. As shown in FIG. 9, a plurality of speed modificationtrials including trials 65 and 66 are performed in order to assess themost likely obstruction. Prior to the corrective action, the pump speedhas a setpoint 67 and a corresponding flow value 68. When an inflowobstruction is present, corrective action comprises gradually decreasingthe pump speed at 70 to produce a gradual increase in flow at 71. Apredetermined minimum speed 72 may preferably have been established bythe physician based on the physiology of the patient, and if the speedreaches that minimum then no further changes would be made. As long asfurther decreases in speed along line 70 generate a correspondingincrease in pump flow along 71, then the speed continues to decrease.When the resultant flow reaches a peak at 73 and then decreases at 74,the reduction in pump speed ceases at 75. Then the speed achieving thehighest flow is adopted at 76.

In the case of a detected outflow obstruction, corrective actioncomprises increasing the pump speed at 80 which results in an increasedpump flow at 81. The increase may continue until either reaching amaximum pump speed 82 as previously determined by a physician or untilpump flow reaches the expected minimum flow.

The plurality of trials and the corrective actions are further describedin the method of FIG. 10. In step 85, an actual flow value and apulsatility index are measured at the current speed setpoint. In step86, the pump speed is reduced by a preset amount. In step 87, a new flowvalue and pulsatility index are measured at the reduced speed. A checkis made in step 88 to determine whether a predetermined number of trialshave been obtained. If not, speed is increased back to the originalsetpoint in step 89 and a return is made to step 85.

Once sufficient trials have been conducted, the trials are classified instep 90. Classification of each trial is performed in accordance withFIG. 8, for example. The classified trials are then examinedstatistically in order to ensure that sufficient data is present toindicate either an inflow obstruction, outflow obstruction, or saturatedflow. In a preferred embodiment, a majority of trials must indicate arespective condition. In step 91, a check is made to determine whether amajority of trials indicate that an inflow obstruction is either likely,possible, or probable. If so, then corrective action to increase pumpflow begins at step 92 by dropping the pump speed by a predeterminedamount. A check is performed in step 93 to determine whether the speedhas been reduced to a predetermined minimum speed. If not, then a checkis performed in step 94 to determine whether the latest drop in speedhas instead caused a flow decrease. If not, then a return is made tostep 92 to drop the speed once again. If a minimum speed is reached instep 93, then the minimum speed is set as a new speed setpoint and themethod returns to point A in FIG. 3. In FIG. 3, the method waits duringa predetermined wait time (T_(EndDiagWait)) in step 110 before returningto normal operation. This periodic return to normal operation ensuresthat nominal operation is utilized whenever possible.

Returning to FIG. 10, in the event that a flow decrease is detected instep 94 then the speed setpoint is set to the last speed that obtained aflow increase in step 96 and a return is made to point A.

If there are not a majority of trials detecting an inflow obstruction instep 91, then a check is made in step 97 to determine whether a majorityof trials indicate a saturated flow. If they do, then pump speed isdropped by a predetermined amount in step 98. A check is performed instep 99 to determine whether a minimum speed has been reached. If not,then a check is made in step 100 to determine whether a predeterminedflow decrease has occurred (i.e., whether the flow has becomeunsaturated). If not, then a return is made to step 98 to drop speedonce again. If a minimum speed is reached in step 99, then the minimumspeed is adopted as a new speed setpoint and the method returns to pointA. If a flow decrease is detected in step 100, then the current speed isused as a new speed setpoint and a return is made to point A.

If a majority of trials do not indicate a saturated flow condition instep 97, then a check is made in step 103 to determine whether amajority of trials indicated that an outflow obstruction is likely,possible, or probable. If not, then the flow problem has not beenproperly diagnosed and the method may retry to diagnose the obstructionin step 104 (e.g., by repeating a new plurality of trials at step 85).If a majority of trials indicate an outflow obstruction, then pump speedis increased by a set amount in step 105. A check is made in step 106 todetermine whether a maximum speed has been reached. If not, then a checkis made in step 107 to determine whether the result flow has reached theexpected minimum flow value. If not, then a return is made to step 105to further increase the speed. If a maximum speed is detected in step106, then the maximum speed is adopted as a new speed setpoint in step108 and a return is made to point A. If the flow reaches the expectedminimum flow value in step 107, then the current speed is used as a newspeed setpoint in step 109 and a return is made to point A.

The present invention can also be understood using a state diagram asshown in FIG. 11. State 115 is a normal pump control state wherein pumpcontrol may be implemented as according to U.S. Pat. No. 7,160,243, forexample. As long as an actual flow remains greater than the expectedminimum flow, operation continues to remain in state 115. When pump flowfalls below the expected minimum flow for greater than timeT_(FlowDiagWait), then a transition is made from state 115 to a flowdiagnostic state 116. A transition is made back from state 116 to state115 when the flow value remains above the expected minimum flow forgreater than T_(FlowDiagWait). State 116 also checks for low flow. Thus,if actual flow falls below the low flow threshold for greater than atime T_(LowFlow) then a transition is made to a low flow alarm state117. A transition would be made back from state 117 to 116 whenever theactual flow remains greater than the low flow threshold for greater thanT_(LowFlow). State 117 monitors for a no flow condition by comparingactual flow with a no flow threshold. If actual flow is less than the noflow threshold for at least time T_(NoFlow) then a transition is made toa no flow alarm state 118. Flow continues to be compared with the noflow threshold and if it remains above the no flow threshold for atleast T_(NoFlow) then a transition is made back to flow diagnostic state116.

While in state 116, actual flow continues to be compared to the expectedminimum flow value and if it remains below it for greater than a timeT_(ObsDiagWait), then a transition is made to diagnose obstruction state120. While in state 120, a plurality of trials are conducted bymodifying the pump speed in order to attempt to classify either aninflow obstruction, outflow obstruction, or saturated flow condition.When an inflow obstruction is detected, a transition is made to state121 for executing a speed reduction action. When an outflow obstructionis detected, then a transition is made to state 123 for executing aspeed increase action. When a saturated flow condition is detected, atransition is made to state 122 for executing a speed reduction action.After the actions in states 121-123, transitions are made to wait state124 wherein the pump continues to operate at a new speed setpoint, thusachieving the best flow results obtainable under current conditions.After a wait time (T_(EndDiagWait)) corresponding to an expected time inwhich conditions may eventually change, a transition is made back tonormal pump control state 115 with a possible reintroduction ofcorrective speed changes if flow again does not exceed the expectedminimum flow.

What is claimed is:
 1. A method of controlling blood flow delivered to apatient by a left ventricle assist device including a pump, comprisingthe steps of: collecting blood flow measurements during operation of thepump; identifying an impaired flow condition when a plurality ofsuccessive blood flow measurements are between an expected flow and alow flow, wherein the low flow would necessitate issuing an alert;during the impaired flow condition, detecting whether an inflowobstruction exists by determining whether a reduction in speed of thepump is correlated with a predetermined increase in the blood flowmeasurements; and if the inflow obstruction is detected, then furtherreducing the speed of the pump to further increase the blood flowmeasurements.
 2. A method of controlling blood flow delivered to apatient by a left ventricle assist device including a pump, comprisingthe steps of: collecting blood flow measurements during operation of thepump; identifying an impaired flow condition when a plurality ofsuccessive blood flow measurements are between an expected flow and alow flow, wherein the low flow would necessitate issuing an alert;during the impaired flow condition, detecting whether an inflowobstruction exists by determining whether a reduction in speed of thepump is correlated with a predetermined increase in the blood flowmeasurements; if the inflow obstruction is detected, then furtherreducing the speed of the pump to further increase the blood flowmeasurements; during the impaired flow condition and if the inflowobstruction is not detected, then detecting whether an outflowobstruction exists by determining whether a reduction in speed of thepump is correlated with a predetermined decrease in the blood flowmeasurements; and if the outflow obstruction is detected, thenincreasing the speed of the pump to increase the blood flowmeasurements.
 3. A system for coupling to a patient to assist blood flowin the patient, comprising: a pump adapted to receive an inflow of bloodfrom the patient and to provide an outflow of blood back to the patient;a motor coupled to rotate the pump at a selectable speed; a controllercoupled to the motor and adapted to drive the motor at a target speedvia a driver signal generated by the controller, wherein the controlleris configured for: collecting blood flow measurements during operationof the pump; identifying an impaired flow condition when a plurality ofsuccessive blood flow measurements are between an expected flow and alow flow, wherein the low flow would necessitate issuing an alert;during the impaired flow condition, detecting whether an inflowobstruction exists by determining whether a reduction in speed of thepump is correlated with a predetermined increase in the blood flowmeasurements; and if the inflow obstruction is detected, then furtherreducing the speed of the pump to further increase the blood flowmeasurements.
 4. A system for coupling to a patient to assist blood flowin the patient, comprising: a pump adapted to receive an inflow of bloodfrom the patient and to provide an outflow of blood back to the patient;a motor coupled to rotate the pump at a selectable speed; a controllercoupled to the motor and adapted to drive the motor at a target speedvia a driver signal generated by the controller, wherein the controlleris configured for: collecting blood flow measurements during operationof the pump; identifying an impaired flow condition when a plurality ofsuccessive blood flow measurements are between an expected flow and alow flow, wherein the low flow would necessitate issuing an alert;during the impaired flow condition, detecting whether an inflowobstruction exists by determining whether a reduction in speed of thepump is correlated with a predetermined increase in the blood flowmeasurements; if the inflow obstruction is detected, then furtherreducing the speed of the pump to further increase the blood flowmeasurements; during the impaired flow condition and if the inflowobstruction is not detected, then detecting whether an outflowobstruction exists by determining whether a reduction in speed of thepump is correlated with a predetermined decrease in the blood flowmeasurements; and if the outflow obstruction is detected, thenincreasing the speed of the pump to increase the blood flowmeasurements.